A type of breathing apparatus which is carried by the user and which is isolated from ambient air, requires a relatively long passageway between parts of the apparatus to permit the recirculating air therein to cool to breathing temperature. In order to arrange the passageway in a compact manner, the passageway is folded in a zigzag manner. This may be accomplished by providing an essentially rectangular bag having partial partitions. Construction of such a bag poses problems. A further problem concerns the fact that the surface of the passageway and the exterior surface of the bag must be of different materials.
The present invention is a solution to these problems.